Force Terrain Details DrawDistance over the 250 limit

ForceGrassDistanceInEditor.cs

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class ForceGrassDistanceInEditor : MonoBehaviour {

	public float distance=250; // 250 is max in terrain settings, but not here
	Terrain terrain;

	void Start () {
		terrain = GetComponent<Terrain>();
		if (terrain==null)
		{
			Debug.LogError("This gameobject is not terrain, disabling forced details distance", gameObject);
			this.enabled=false;
			return;
		}

	}

	// WARNING: this runs update loop inside editor, you dont need this if you dont change the value
	void Update()
	{
		terrain.detailObjectDistance = distance;
	}
}